The present invention relates generally to medical infusion pumps, and more particularly to a curvilinear peristaltic pump having a plurality of cam driven pumping fingers which sequentially engage a segment of resilient tubing to facilitate the flow of a liquid therethrough.
There is currently known in the prior art various types of peristaltic pumps which are typically used in medical applications for facilitating the metered intravenous infusion of a medicament into a patient. In addition to being used for infusion applications, prior art peristaltic pumps are also used for withdrawing fluids such as in a wound drainage system. These prior art pumps operate in a positive manner and are capable of generating substantial outlet pressures. The peristaltic pumps known in the prior art generally fall within one of two categories, i.e., linear peristaltic pumps and rotary peristaltic pumps. Conventional linear and rotary peristaltic pumps each typically have a section of resilient tubing positioned between a wall and a set of rollers or reciprocating pushers that progressively compress sections of the tubing to facilitate the pumping of a liquid therethrough.
More particularly, typical linear peristaltic pumps include those described in U.S. Pat. No. 2,877,714 (Sorg, et al.), U.S. Pat. No. 4,671,792 (Borsannyi), U.S. Pat. No. 4,893,991 (Heminway, et al.), and U.S. Pat. No. 4,728,265 (Canon). While generally effective, these prior art linear peristaltic pumps are large, complex and cumbersome, requiring a drive shaft parallel to a resilient tube and a plurality of cams along the drive shaft to move respective ones of a plurality of pushers toward and away from the tube.
Rotary peristaltic pumps known in the prior art generally disposed a resilient tube along a circular path, with a plurality of rollers mounted around the circumference of a circular rotor sequentially rolling along the tube to occlude the same and force liquid therethrough. Typical rotary peristaltic pumps include those described in U.S. Pat. No. 4,886,431 (Soderquist, et al.) and U.S. Pat. No. 3,172,367 (Kling). Though also generally effective, these pumps often have relatively low efficiencies and impose high shear and tension stresses on the tube, thus causing internal tube wall erosion or spallation. As a result, the tube may eventually be permanently deformed so that it becomes flattened into a more oval shape and carries less liquid, i.e., provides a decreased level of fluid flow therethrough.
In addition to the above-described linear and rotary peristaltic pumps, there is also known in the prior art another type of peristaltic pump having a tube arranged along a circular path with a cam member within the circle sequentially moving a plurality of blunt pushers or fingers outwardly to sequentially compress the tube from one end of the path to the other. These types of peristaltic pumps include those described in German Patent No. 2,152,352 (Gonner) and in Italian Patent No. 582,797 (Tubospir). Though these types of pumps tend to be less complex than linear peristaltic pumps, the pressure imposed by the blunt fingers typically reduces tube life, and sometimes causes internal tube wall erosion or spallation, thus resulting in particulate matter getting into the fluid stream. Additionally, tubes with different wall thicknesses cannot be accommodated by these particular prior art pumps. In this respect, with thinner than standard tubes, the fingers will not properly occlude the tube. Conversely, with thicker than standard tubes, the tube will close prematurely and be subject to excessive compression, thereby requiring higher cam drive power and causing excessive wear on the cam and tube.
In recognition of the deficiencies associated with the prior art peristaltic pumps described above, Applicant developed the curvilinear peristaltic pump disclosed in U.S. Pat. No. 5,575,631 (Jester) and U.S. Pat. No. 5,683,233 (Moubayed, et al) and PCT Application No. PCT/US97/03676 (Moubayed, et al.), the disclosures of which are incorporated herein by reference. This particular curvilinear peristaltic pump of the Applicant constituted an improvement over those known in the prior art by providing greater simplicity, small size, low drive power requirements and the ability to accommodate resilient tubes of varying wall thickness while reducing wear and internal erosion of the resilient tube. More particularly, this particular curvilinear peristaltic pump of the Applicant comprises a concave, curved platen for supporting a resilient tube, a multi-lobe cam rotatable about the center of the platen concavity, and a plurality of pump fingers which ride on the cam as cam followers and are guided to move in a radial direction toward and away from the platen. When the cam is rotated, the pump finger closest to the highest area (widest lobe) on the cam in the direction of rotation is moved outwardly in a radial direction to squeeze the tube against the platen. As the cam continues to rotate, the succeeding pump finger squeezes the tube as the preceding pump finger occludes the same, thus forcing the liquid in the tube to flow in the direction of cam rotation. As the cam rotation continues, the subsequent pump fingers sequentially squeeze the tube to push liquid and then occlude the tube, with the pump finger just behind the lobe moving away from the tube and allowing the same to expand and fill with the liquid.
Though this curvilinear peristaltic pump of the Applicant overcomes many of the deficiencies of the prior art peristaltic pumps, the design features of such pump give rise to certain inefficiencies in its operation. In particular, the motor, pulley and drive belt used to rotate the cam create a susceptibility for slight amounts of forward rotation or reverse rotation (roll back) of the cam upon the deactivation of the motor. Such slight forward or reverse rotation of the cam results in the engagement of the pump fingers to the tube in a manner causing an undesirable positive flow or backflow of liquid therewithin subsequent to the deactivation of the motor. As such, in this curvilinear peristaltic pump of the Applicant, power must be continuously supplied to the motor for purposes of preventing any unwanted rotation of the cam. As will be recognized, the need to constantly maintain power to the motor substantially increases its power consumption (e.g., reduces the life of any batteries used to supply power to the motor).
In addition to the foregoing, in Applicant""s existing curvilinear peristaltic pump, a xe2x80x9cpump cyclexe2x80x9d occurs when the first through the last pump fingers along the tube move toward and away from the platen. During each xe2x80x9cpump cyclexe2x80x9d, the engagement of the pump fingers against the tube in the above-described manner forces liquid therethrough. However, due to the configuration of the cam and the inability of the drive unit to selectively adjust the rotational speed thereof, there is a xe2x80x9cdead pump phasexe2x80x9d between the pump cycles in Applicant""s existing curvilinear peristaltic pump wherein liquid is not being forced through the tube. As will be recognized, it is significantly more desirable if the liquid were to flow through the tube at a more uniform, steady rate. The operational efficiency of Applicant""s existing curvilinear peristaltic pump would also be increased if it were to include structures which stabilize the length of the tube in the pump chamber and prevent a backflow of liquid within the tube upon a discontinuation of positive liquid pressure therewithin. The present invention addresses and overcomes the deficiencies of Applicant""s existing curvilinear peristaltic pump, as well as the other peristaltic pumps currently known in the prior art.
In accordance with the present invention, there is provided a curvilinear peristaltic pump for facilitating the pumping of a liquid through a length of resilient tubing. The pump comprises a housing including a pair of housing halves which are attached to each other. In addition to the housing, the pump comprises a platen member which is pivotally connected to the housing and movable between an operative position and a non-operative position relative thereto. The platen member defines an arcuate, generally concave inner surface, and includes an over-the-center latch mechanism for maintaining the same in its operative position relative to the housing.
The present pump further comprises a rotatable cam which is disposed within the housing and rotatable about the approximate center of the concavity of the inner surface of the platen member. The rotation of the cam is facilitated by a drive unit of the pump which is also disposed within the housing. The drive unit is mechanically coupled to the cam such that the activation of the drive unit results in the concurrent rotation of the cam in a first direction, and the deactivation of the drive unit maintains the cam in a set position. In the preferred embodiment, the drive unit comprises a cam shaft which extends from the cam and includes a worm gear attached thereto. In addition to the cam shaft and worm gear, the drive unit comprises an electric motor having a rotatable motor shaft extending therefrom which includes a worm mounted thereto. The worm is itself cooperatively engaged to the worm gear. Importantly, the engagement between the worm and the worm gear results in the rotation of the cam in the first direction upon the activation of the motor, with such engagement also eliminating any rotation of the cam upon the deactivation of the motor. The electric motor of the drive unit is preferably powered by multiple batteries (e.g., C-cell batteries) which are stored within the housing.
The present pump further comprises a plurality of pump fingers which are movably attached to the housing and are arranged in side-by-side relation to each other so as to define a row. Each of the pump fingers has a first end which is cooperatively engaged to the cam and a second end which is disposed in spaced relation to the platen member. Attached to the housing is a pliable, transparent membrane of the pump which covers the second ends of the pump fingers and is used to prevent moisture from leaking into the interior of the housing. As such, the second ends of the pump fingers are covered by the membrane, and are disposed in substantially equidistantly spaced relation to the inner surface of the platen member when in its operative position. The membrane is exposed when the platen member is in its non-operative position. Each of the pump fingers preferably includes a plurality of roller members rotatably mounted within and protruding from the first end thereof, with the pump fingers being cooperatively engaged to the cam via the roller members.
In the present pump, the cam is configured to sequentially move the pump fingers radially outwardly toward and inwardly away from the inner surface of the platen member when rotated in the first direction by the drive unit. In this respect, a portion of the tubing may be extended between the inner surface of the platen member and the membrane (and hence the second ends of the pump fingers) such that the sequential movement of the pump fingers toward and away from the platen member results in liquid within the tubing being pumped in the first direction of rotation of the cam. As will be recognized, since the pumping of the liquid through the tubing is dependent upon the sequential engagement of the pump fingers thereagainst and the movement of the pump fingers is dependent upon the rotation of the cam, the deactivation of the motor which eliminates any rotation of the cam due to the engagement between the worm and the worm gear assists in preventing any positive flow or backflow of liquid through the tubing.
In the present pump, the sequential movement of each of the pump fingers of the row toward and away from the platen member by the rotation of the cam defines a pump cycle. In the preferred embodiment, the cam is profiled or shaped so as to act against the first ends of the pump fingers in a manner causing the second ends thereof to engage the tubing such that the flow rate of liquid therethrough is substantially constant throughout each pump cycle. Such constant flow rate is achieved by forming the cam as a four lobe cam. In addition to the cam being shaped to provide a substantially constant flow rate throughout each pump cycle, the pump of the present invention is preferably provided with a motor speed control unit which is operable to selectively increase and decrease the rotational speed of the cam at prescribed intervals. More particularly, the motor speed control unit is operable to increase the rotational speed of the cam in the first direction between pump cycles for purposes of substantially eliminating the dead pumping phase which normally exists between pump cycles.
The motor speed control unit of the present pump is disposed within the housing and comprises an optical sensor which is electrically connected to the motor. The optical sensor is adapted to transmit a beam of light and sense any interruptions therein. In this respect, the optical sensor includes a light beam transmitter which is adapted to generate a beam of light, and a light beam receiver which is adapted to receive or sense the beam of light generated by the light beam transmitter. In addition to the optical sensor, the motor speed control unit comprises an encoder wheel which is attached to the cam shaft and rotatable thereby. The encoder wheel includes a plurality of encoder arms extending radially therefrom and is oriented relative to the optical sensor such that the encoder arms intermittently interrupt the beam of light during the rotation of the encoder wheel by the cam shaft. Importantly, the number and size of the encoder arms is selected such that interruptions in the beam of light caused thereby correspond to pump cycles, with the optical sensor being operable to determine the beginning and end of each pump cycle and increase the power to the motor and hence the rotational speed of the cam between pump cycles. As will be recognized, the increased rotational speed of the cam between pump cycles substantially reduces the dead pump phase, thereby providing a more uniform rate of liquid flow through the tubing.
The present pump further comprises a plurality of pinch members which are movably attached to respective ones of the pump fingers and protrude from the second ends thereof. Each of the pinch members is biased radially outwardly toward the inner surface of the platen member and operable to substantially occlude the tubing when the pump finger to which it is attached is moved radially outwardly to a position closest to the inner surface of the platen member. To facilitate the attachment of a pinch member thereto, each of the pump fingers is provided with a transverse slot which is disposed within the second end thereof and transitions into a transverse cavity therewithin. Each of the pinch members preferably comprises a base portion which is disposed within the transverse cavity and a finger portion which extends from the base portion into the transverse slot. The finger portion defines a finger tip which protrudes from the second end of the pump finger. Extending between the base portion and the wall of the transverse cavity disposed furthest from the finger portion is a biasing spring of the pinch member. The present pump further comprises a pair of pressure sensor members which are oriented within the housing adjacent respective ends of the row of pump fingers for engaging the tubing and generating electrical signals corresponding to the degree of compression or expansion thereof when acted upon by the pump fingers and pinch members.
The pump constructed in accordance with the present invention is preferably used in conjunction with a tubing assembly which is releasably attachable to the housing. The tubing assembly comprises a length of substantially straight, resilient tubing which is preferably fabricated from polyvinyl chloride (PVC). Attached to the tubing is a tubing locator pin and a shut-off valve which is operable to selectively obstruct the flow of liquid through the tubing in a direction opposite the first direction of rotation of the cam. The tubing locator pin and the shut-off valve are removably insertable into respective ones of a pair of recesses formed within the housing outwardly of each of the opposed ends of the row of pump fingers. Importantly, the tubing locator pin and the shut-off valve are attached to the tubing at locations whereat a portion of the tubing is extended over the second ends of the pump fingers when the tubing locator pin and the shut-off valve are removably inserted into their respective recesses within the housing. When the platen member is in its operative position, the tubing is extended between the second ends of the pump fingers and the platen member such that the sequential movement of the pump fingers toward and away from the platen member results in liquid within the tubing being pumped in the first direction of rotation of the cam.
In the present pump, the tubing locator pin and the shut-off valve of the tubing assembly are removably insertable into their respective recesses within the housing when the platen member is in its non-operative position. As indicated above, the portion of the tubing extended over the second ends of the pump fingers by the insertion of the tubing locator pin and the shut-off valve into their respective recesses within the housing is captured between the second ends and the inner surface when the platen member is moved to its operative position.
In the preferred embodiment, the shut-off valve of the tubing assembly itself comprises a valve body having an opening therein for permitting the passage of the tubing therethrough. Movably attached to the valve body is a pinch arm which is engagable to the tubing passing through the opening. The pinch arm is movable between an open position whereat the tubing passing through the valve body is only partially collapsed thereby and not compressed by the pinch arm which allows for the flow of liquid through the tubing, and a closed position whereat the tubing passing through the valve body is completely collapsed by the pinch arm acting thereagainst which prevents the flow of liquid through the tubing. The shut-off valve further includes a biasing member which normally biases the pinch arm to the closed position, with the biasing member preferably comprising a spring which extends between the valve body and the pinch arm. The pinch arm of the shut-off valve itself includes a breakable detent tab formed thereon which maintains the pinch arm in its open position. The removal or breakage of the detent tab from the pinch arm results in the movement of the pinch arm to its closed position.
In the present pump, the platen member is sized and configured to move the pinch arm from its closed position to its open position when the platen member is moved to its operative position. Additionally, the platen member is pivotally connected to the housing at a location whereat the movement of the platen member from its non-operative position to its operative position results in the occlusion of the tubing by at least one of the pinch members prior to the movement of the pinch arm of the shut-off valve from its closed position to its open position by the platen member.
In addition to the above-described pressure sensor members, the present pump is provided with a platen sensor which is disposed within the housing and operable to detect when the platen member is in the operative position. More particularly, the platen sensor comprises a Hall effect sensor which includes a magnet disposed within the over-the-center latch mechanism of the platen member. In addition to the magnet, the platen sensor includes a magnetic field detector which is disposed within the housing. The magnet and the magnetic field detector are oriented so as to be disposed directly adjacent each other when the platen member is in its operative position. The pump also includes a tubing sensor which is disposed within the housing and operable to detect when the tubing is extended over the membrane. More particularly, whereas the platen sensor is tripped by the movement of the platen member to its operative position, the tubing sensor is tripped by the insertion of the tubing locator pin into its corresponding recess within the housing. In the preferred embodiment, the platen sensor and the tubing sensor are electrically connected in series such that the drive unit may not be activated until the tubing is extended over the membrane and the platen member is in its operative position.
Advantageously, the tubing locator pin and shut-off valve of the tubing assembly may be added or attached to lengths of resilient tubing of differing diameters. Additionally, the use of off-the-shelf straight line, continuous PVC tubing in the present tubing assembly as opposed to a segment of silicone tubing having segments of PVC tubing adhesively secured thereto as is required by many prior art peristaltic pumps substantially reduces the costs associated with the present tubing assembly, in addition to providing increased reliability due to the absence of any adhesive joints. In the tubing assembly, the shut-off valve attached to the tubing is maintained in its open position during shipment so as not to cause any premature deformation in the tubing. When the present pump and accompanying tubing assembly are ready for use, the detent tab is broken away from the pinch arm of the shut-off valve, thus causing the same to assume its normally closed position upon the tubing.